Cytosol

The accumulation of misfolded proteins in the cytosol and nucleus of
neuronal cells leads to neurodegenerative disorders. Polyglutamine diseases
are caused by polyglutamine-expanded proteins, whereas mutations in
superoxide dismutase 1 lead to amyotrophic lateral sclerosis.

Rv3619c and Rv3620c are the secretory, antigenic proteins of the ESAT-6⁄CFP-10 family ofMycobacterium tuberculosisH37Rv. In this article, we
show that Rv3619c interacts with Rv3620c to form a 1 : 1 heterodimeric
complex with a dissociation constant (Kd) of 4.8·10
)7
M. The thermal
unfolding of the heterodimer was completely reversible, with a Tm of
48C.

Humanether a` go-go potassium channels (hEAG1) open in response to
membrane depolarization and they are inhibited by Ca
2+
⁄calmodulin
(CaM), presumably binding to the C-terminal domain of the channel sub-units. Deletion of the cytosolic N-terminal domain resulted in complete
abolition of Ca
2+
⁄CaM sensitivity suggesting the existence of further CaM
binding sites.

Cytosolic 5¢-nucleotidase (cN-II), which acts preferentially on 6-hydroxypu-rine nucleotides, is essential for the survival of several cell types. cN-II
catalyses both the hydrolysis of nucleotides and transfer of their phosphate
moiety to a nucleoside acceptor through formation of a covalent phospho-intermediate.

We investigated the changes in the oxidative stress response of yeast cells
suffering mitochondrial dysfunction that could impair their viability.
First, we demonstrated that cells with this dysfunction rely exclusively on
cytosolic thioredoxin peroxidase I (cTPxI) and its reductant sulfiredoxin,
among other antioxidant enzymes tested, to protect them against H2O2
-induced death.

Cytosolic phospholipase A2
-a (cPLA2
-a) is a calcium-activated enzyme involved in agonist-induced arachidonic
acid release. In endothelial cells, free arachidonic acid is
predominantly converted into prostacyclin, a potent vaso-dilator and inhibitor of platelet activation. As the rate-lim-iting step in prostacyclin production is the generation of free
arachidonic acid by cPLA2-a, this enzyme has become an
attractive pharmacological target and the focus of many
studies.

Small Hsps (sHsps) and the structurally related eye lens
a-crystallins are ubiquitous stress proteins that exhibit ATP-independent molecular chaperone activity. We studied the
chaperone activity of dodecameric wheatTaHsp16.9C-I, a
class I cytosolic sHsp from plants and the only eukaryotic
sHsp for which a high resolution structure is available,
along with the related wheat proteinTaHsp17.8C-II, which
represents the evolutionarily distinct class II plant cytosolic
sHsps. Despite the available structural information on
TaHsp16.

Information on the regulation and structure–function rela-tion of enzymes involved in DNA precursor synthesis is
pivotal, as defects in several of these enzymes have been
found to cause depletion or deletion of mitochondrial DNA
resulting in severediseases.Here, the effect of aminoacid106
on the enzymatic properties of the cell-cycle-regulated
human cytosolic thymidine kinase 1(TK1) is investigated.

In a previous study, the S100A8/A9 protein, a Ca2+- and arachidonic acid-binding protein, abundant in neutrophil cytosol, was found to potentiate the activation of the redox component of the O2– generating oxidase in neutrophils, namely the membrane-bound ﬂavocytochrome b, by the cytosolic phox proteins p67phox, p47phox and Rac ` (Doussiere J., Bouzidi F. and Vignais P.V. (2001) Biochem. Biophys. Res. Commun. 285, 1317–1320). This led us to check by immunoprecipitation and protein fractionation whether the cytosolic phox proteins could bind to S100A8/A9.

Glutathione (GSH) conjugating enzymes, glutathioneS-transferases (GSTs),
are present in different subcellular compartments including cytosol,
mitochondria, endoplasmic reticulum, nucleus and plasma membrane. The
regulation and function of GSTs have implications in cell growth, oxidative
stress as well as disease progression and prevention.

Cytosolic sulfotransferase (SULT) SULT2B1b had previously been charac-terized as a cholesterol sulfotransferase. Like human SULT2B1, mouse
SULT2B1b contains a unique, 31 amino acid C-terminal sequence with a
proline⁄serine-rich region, which is not found in members of other SULT
families. To gain insight into the functional relevance of this proline⁄ser-ine-rich region, we constructed a truncated mouse SULT2B1b lacking the
31 C-terminal amino acids, and compared it with the wild-type enzyme.

TheArabidopsis thalianagenome contains four genes encoding NADP-malic enzymes (NADP-ME1–4). Two isoenzymes, NADP-ME2 and
NADP-ME3, which are shown to be located in the cytosol, share a
remarkably high degree of identity (90%). However, they display different
expression patterns and show distinct kinetic properties, especially with
regard to their regulation by effectors, in both the forward (malate oxida-tive decarboxylation) and reverse (pyruvate reductive carboxylation) reac-tions.

Cytochromec(cyto-c), added to isolated mitochondria, activates the oxida-tion of extramitochondrial NADH and the generation of a membrane
potential, both linked to the activity of the cytosolic NADH/cyto-celectron
transport pathway.